The present invention relates to the field of industrial organic synthesis, particularly to the production of phenol and acetone by the cumene method.
A known method for the production of phenol and acetone by the oxidation of cumene with atmospheric oxygen, followed by the acid-catalyzed decomposition of cumene hydroperoxide, makes it possible to obtain both target products (acetone and phenol) at a high yield (Khruzhalov B. D., Golovanenko B. N., Co-production of phenol and acetone, Moscow, GosKhimIzdat, 1964). This method is practiced widely in the production of these products, and is the main method used globally.
Sulfuric acid is used as a catalyst for decomposing cumene hydroperoxide (CHP) at operating plants where phenol and acetone are produced by the cumene method. A method is known for decomposing cumene hydroperoxide by using phenol-2,4-disulfonic acid (also known as 4-hydroxybenzene-1,3-disulfonic acid) (Russian Authors' Certificate No. 213892). The decomposition process is performed in one stage at a catalyst concentration of 0.1 to 0.5 wt % and a temperature of 50° C. This method makes it possible to reduce the formation of phenolic resins (also referred to as “heavies”). However, this reduction is not significant in comparison with the two- to three-fold reduction in the phenolic resin yield levels attained by other known methods, which are further described below.
There are known methods for producing phenol and acetone in which, in order to reduce the yield of phenolic resins, cumene oxidation products containing cumene hydroperoxide (CHP), cumene, and dimethylphenylcarbinol (DMPC, also referred to as dimethylbenzyl alcohol (DMBA)) are cleaved in two stages in the presence of sulfuric acid. The first stage involves decomposition of most (97 to 99%) of CHP and synthesis of dicumyl peroxide (DCP) from DMPC and CHP at 55 to 80° C. The second stage involves adding acetone to the resulting reaction mixture containing phenol, acetone, DMPC, and DCP at a temperature of 80 to 120° C. The acetone is added in an amount equal to 1.5 to 1.8 times its initial concentration. This process is accompanied by the cleavage of the DCP formed in the first stage, decomposition of the residual CHP, and dehydration of the residual DMPC (Russian Patent Nos. 2,068,404 and 2,121,477).
The aforementioned methods for decomposing CHP in two stages make it possible to markedly reduce the amount of byproducts in comparison with the one-stage decomposition (resin yield: 25 kg/t of phenol). At the same time, the amount of the hydroxyacetone (HA) byproduct remains high in these improved two stage processes (for example, more than 1000 ppm).
Hydroxyacetone is a source of 2-methylbenzofuran, which is difficult to separate from phenol and which has an adverse effect on the color indexes of products made from impure commercial-grade phenol. Hydroxyacetone can be removed from phenol, for example, by an alkaline treatment, but this makes the technology of the process more complicated (Vasilieva I. I., Zakoshansky V. M., Collection of articles titled “Petrochemical and Oil Refining Processes,” SPb, Giord, 2005, pp. 89-154, 344). Moreover, the existing phenol purification technology requires 1.3 to 2.5 kg/kg of phenol (the molar ratio is from 1:1 to 1:2) to be used in the reaction with hydroxyacetone.
A method is known for decomposing CHP in two stages (Russian Patent No 2,142,932, U.S. Pat. No. 6,057,483). This CHP decomposition process is carried out in three serially arranged mixing reactors in the first stage, and a displacement reactor in the second stage. The CHP is decomposed in the first stage under conditions close to isothermal (that is, at a temperature of 47 to 50° C. and a concentration of 0.018 to 0.020 mass % for the sulfuric acid catalyst), while the reaction mass is additionally diluted with acetone in an amount equal to 5 to 8 mass % relative to the amount of supplied CHP. Almost all of the CHP reacts in the process, and DCP forms from part of CHP and DMPC.
The process in the second stage is carried out while the sulfuric acid is partially neutralized with ammonia, forming ammonium hydrosulfate at a temperature of 120 to 140° C., and while some water is added. The concentration of sulfuric acid is 0.009 to 0.010 mass %. The CHP and DCP are decomposed in a reaction medium containing phenol and acetone, both of which are formed from the CHP. Additional acetone may optionally be added to the reactor if desired.
A method is known for decomposing technical-grade CHP in serially connected reactors in two stages so that the CHP is partially decomposed and dicumyl peroxide is formed in the first stage at a temperature of 40 to 65° C. in the presence of 0.003 to 0.015 mass % of sulfuric acid as a catalyst, followed by the decomposition of CHP and DCP in the second stage at a temperature of 90 to 140° C. The process is performed using excess phenol in the reaction medium at a phenol/acetone molar ratio greater than 1, and preferably from 1.01 to 5. The excess phenol is produced either by driving off acetone or by adding phenol to the reaction medium (see, for example, Russian Patent No. 2,291,852). When technical-grade CHP is decomposed under these conditions, the hydroxyacetone yield is reduced to 0.04 mass % (400 parts per million (ppm)) in the reaction medium, whereby the quality of the commercial-grade phenol is markedly improved. However, application of this method is premised on the use of phenol that has been purified in a phenol purification system, and the purification of phenol involves additional manufacturing steps and power consumption.
Some disadvantages of the prior art methods are the presence of hydroxyacetone (HA) in the resulting phenol, and in some cases the need for quenching excess sulfuric acid during the second stage. The presence of HA has an adverse effect on the phenol quality while the quenching of sulfuric acid results in additional complexity and processing steps as well as higher operating costs in the process. Therefore, there is a need for a method to further reduce the amount of HA in the phenol produced and to eliminate entirely the sulfuric acid quenching step or at least substantially reduce the amount of neutralization agent required in the quenching step.